We demonstrated that cell organelles called microperoxisomes, owing to their size and peroxidase content, are abundant in retinal pigment epithelium of humans, monkeys, domestic fowl, frogs, mice and rats. The number of microperoxisomes in the retinal pigment epithelium increased nearly three fold in animals which had low serum cholesterol and lipids following treatment with nafenopin. Therefore, microperoxisomes may play an important role in lipid metabolism. We found that microperoxisomes are not related to the development of lysosomes or melanin granules. They are normal in the mouse model for the Chediak-Higashi syndrome even though the lysosomes and melanin granules are defective. We compared the digestive mechanisms and melanogenesis of the pigment epithelium of beige (bg/bg) and black (plus/plus) mice of the C57 BL/6N strain. We localized acid phosphatase within the pigment epithelial cells and discovered defects in the packaging of this important digestive enzyme in the mutant (beige) mouse. We found more relation between melanogenesis and lysosome formation than was shown previously.